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Megalith - Current NFB Class A Power Amplifier

Introduction

My first set of electronics started in 1979 as an experiment based on a design published in the French magazine "L'Audiophile No. 10" by Jean Hiraga.

Modified Version of Hiraga's Class A Amplifier

Although a Class A triode push-pull or single ended tube amplifier might have been the better choice in those days (and possibly still today), I was highly attracted by the new developed Hitachi FET-Devices. As owner of the high efficient Onken-Mahul System, most of the time 1 watt with peaks to 8 watt were absolutely sufficient. So, I decided to simplify the modified version of Hiraga's Class A Amplifier once more (reduction of open-loop gain and use of less discrete components) and settled for a class A operation of 8 watt.

FET Amplifier No. 1

Power Supply for FET Amplifier No. 1

Preamplifier, FET Power Amplifier and X-over No. 1

This FET Power Amplifier No. 1 was produced in 1980 for several music enthusiast and friends. Today, after 30 years one of these power amplifiers is still in use and according to the owner it performs (after refurbishing) still better than many high rated commercial amplifiers.

RBS Megalith: Real Batterie Supply Solution

Encouraged by the friendly, direct and immediate sound of the FET Amplifier No.1 and repeated requests from some of the owners to design an improved successor, I finally decided in 2000 to start the task. But, where should the existing design be improved?

Suspecting that the ear compensates for amplifier distortion, when it is simple in nature over the entire power range, but does not like distortion of high harmonic order, it became immediately clear I should primarily improve the power supply. The only way to accomplish this is the use of regulated power supplies or accumulators. Since I wanted an excellent and simple solution, I chose the accumulators.

Other areas of improvements are a further reduction in components and the use of more linear semiconductors.

RBS Megalith - FET Power Amplifier No. 2

Along with the effort of improving the existing FET Power Amplifier No.1, I considered other topologies which may have a similar performance.

These alternative design uses, more or less, the same number of components.


Although all designs look simple, reliable comparison and assessment require a lot of time and standing power. Somewhat limited in time, I continued with the well known improved Megalith design in order to avoid any tonal disaster for my friends.

Overview

Power Amplifier

Battery Supply Unit